1. Field of the Invention
The present invention relates to heat sinks and, more particularly, to a heat sink having a heat pipe suitable for cooling a semiconductor device or the like.
2. Description of the Related Art
In recent years, as a cooling device for cooling a semiconductor device generating a large amount of heat, a heat sink using a heat pipe having an extremely high heat transfer performance. In a conventional heat pipe, heat is absorbed in a heat absorbing part by a cooling medium sealed within a pipe or a flat plate-shaped container being evaporated in the heat absorbing part. The evaporated cooling medium moves to a heat radiating part and cooled so as to be liquefied, resulting in the heat absorbed in the heat absorbing part being radiated. The cooling medium liquefied in the heat radiating part spreads into a mesh or fiberform member referred to as a wick, and moves through the wick according to a capillary phenomenon and returns to the heat absorbing part, and is evaporated again and moves to the heat radiating part.
As a cooling medium enclosed in a heat pipe, pure water is used in many cases. In order to lower an evaporation temperature and to make an operation temperature low, the interior of the heat pipe in which a cooling medium is enclosed may be set to a reduce pressure. Moreover, a container of a heat pipe is formed of copper or aluminum, which has a high thermal conductivity, in many cases.
When arranging a heat pipe as a heat sink, it is general to increase a heat radiation efficiency by attaching heat radiation fins to a heat radiation part. In order to increase the heat radiation efficiency further, the heat radiation part may be enlarged. For example, there may be a structure in which a heat pipe is formed as a flat plate-shaped container and heat radiation fins are attached to one of flat surfaces. Additionally, there is a structure in which a long heat pipe is accommodated in a small volume by bending the bar-like heat pipe in a U-shape.
It is also suggested to acquire a higher heat radiation efficiency by increasing a volume inside a heat pipe by making the heat pipe itself into a three-dimensional construction. In order to increase the volume inside the heat pipe, it is considered to make the heat pipe itself to have a three-dimensional construction.
For example, there is suggested a heat sink having a structure in which a rod-like heat pipe is bent in a channel shape so form a three-dimensional construction and opposite ends thereof are inserted into a base member forming heat radiation fins (for example, refer to Patent Document 1). Additionally, there is suggested a heat pipe having a structure in which one heat pipe is connected perpendicular to another heat pipe and interiors of the heat pipes are caused to communicate with each other (for example, refer to Patent Documents 2 and 3).
Patent Document 1: Japanese Laid-Open Patent Application No. 6-13511
Patent Document 2: Japanese Laid-Open Patent Application No. 7-142652
Patent Document 3: Japanese Laid-Open Patent Application No. 7-263601
In the heat sink disclosed in the above-mentioned Patent Document 1, a three-dimensional structure is formed by bending a heat pipe. However, since a wick is attached on an inner surface of the heat pipe, the wick may be cut when bending the heat pipe. If the wick is cut, a flow of the cooling medium is blocked, which results in a decrease in the cooling efficiency. Additionally, it is difficult to bend a flat plate-shaped heat pipe unlike rod-like heat pipe.
Although the heat sinks disclosed in Patent Documents 2 and 3, have a flat plate-shaped heat pipe connected with a plurality of flat plate-shaped heat pipes perpendicularly, there is no description of a structure of a wick. For example, it is assumed that two flat plate-shaped heat pipes 1A and 1B are connected with each other as shown in FIG. 1. In this case, it is needed to connect wicks 2A and 2B attached to inner surfaces to each other. However, if the wicks 2A and 2B are connected at a connecting part of the heat pipes, a liquid transportation path length to a heat receiving part (that is, a cooling part contacting a heat generating member 3) becomes long. Thus, there is a problem in that a thermal transportation efficiency is decreased due to a cooling medium returning a heat receiving part along the wick by turning to a liquid. In FIG. 1, flows of the cooling medium are indicated by arrows. Additionally, if the wicks are not connected well at the connecting part, and in a top heat in which the heat receiving part is located up or side (that is, an arrangement in which a heat generating member is attached to an upper portion or a side portion of the heat pipe), a flow of the liquid cooling medium is blocked at a cut portion of the wicks, which causes a problem in that the cooling medium cannot be transported to the heat receiving part.
As mentioned above, although there were suggestions to connect heat pipes three-dimensionally, they are not a connection structure in which a consideration is given to a flow of a cooling medium inside. There is no consideration of a connection method of wicks in a plurality of heat pipes at all.